Question

我们有两个表，一个带有ID，另一个带有名称。有些id不是必需的（可以为空），例如：

rowId item1Id, item2Id, item3Id (item3Id can be null)

在我们加入这两个表后，我们得到了id和名字。但是，如果item3 Id为null，则不显示该行。

一些数据：

表1

rowId，item1Id，item2Id，item3Id

1,2,3,4

2,1,5，NULL

在我们的例子中，我们得到一行（1行）

因此，如果它在表2中没有存在，并且没有显示该行，但我们希望显示null。所以当我们离开连接这两个表时，结果应该有2行。

这是sql：

SELECT Recipes.recipeId, Recipes.userId,Users.firstName + ' ' + Users.lastName as userName,  servingTypeId,
Codings.coding as servingType, categoryId, Codings_2.coding as healthAspects, continentId,
Codings_3.coding as continent, countryId, CodingsAssociated.coding as country, typeOfPreparationId,
Codings_4.coding as typeOfPreparation, flavourId, Codings_5.coding as flavour, preparationSkillId,
Codings_6.coding as preparationSkill, seasonId,  activePreparationTime,
overallPreparationTime, isLocalDelight, servings, Codings_7.coding as season ,
calories, youTubeId, datePosted, isComposite, Recipes.isApproved, Recipes.timestamp, title,
localDelightRegion, otherFeatures, cookingInstructions 
      FROM Recipes LEFT OUTER JOIN

      Codings ON Recipes.servingTypeId = Codings.codingKeyId LEFT OUTER JOIN
      Codings as Codings_2 ON Recipes.categoryId = Codings_2.codingKeyId LEFT OUTER JOIN
      Codings as Codings_3 ON Recipes.continentId = Codings_3.codingKeyId LEFT OUTER JOIN
      CodingsAssociated ON Recipes.countryId = CodingsAssociated.codingKeyId LEFT OUTER JOIN
      Codings as Codings_4 ON Recipes.typeOfPreparationId = Codings_4.codingKeyId LEFT OUTER JOIN
      Codings as Codings_5 ON Recipes.flavourId = Codings_5.codingKeyId LEFT OUTER JOIN
      Codings as Codings_6 ON Recipes.preparationSkillId = Codings_6.codingKeyId LEFT OUTER JOIN
      Codings as Codings_7 ON Recipes.seasonId = Codings_7.codingKeyId  LEFT OUTER JOIN
      RecipesTranslations ON Recipes.recipeId = RecipesTranslations.recipeId LEFT OUTER JOIN
      Users ON Recipes.userId = Users.userId

      WHERE CodingsAssociated.languageId = @languageId AND Codings.languageId = @languageId
      AND Codings_2.languageId = @languageId AND Codings_3.languageId = @languageId
      AND Codings_4.languageId = @languageId AND
      Codings_5.languageId = @languageId AND Codings_6.languageId = @languageId AND RecipesTranslations.languageId = @languageId
      AND Codings_7.languageId = @languageId

例如因为seasonId有时为null，所以Codings_7.coding的连接没有显示，但是我也不会显示这些行，其中id为null，名称也为null。

Answer 1

很难说，这里要问的是什么，但我认为你需要做一个外连接，并且从tsql标签我想你使用MS SQL服务器，所以在这里你去：http://msdn.microsoft.com/en-us/library/aa213228(v=sql.80).aspx < / p>

e.g：

SELECT *
FROM table1 a LEFT OUTER JOIN table2 b 
ON a.id_to_join_on = b.id_to_join_on

Answer 2

正如Nikola Markovinović所述，您需要将where条件移动到连接条件

这里你的选择更正了：

SELECT
   Recipes.recipeId,
   Recipes.userId,
   ---
   cookingInstructions 
FROM
   Recipes
   LEFT OUTER JOIN Codings ON
      Recipes.servingTypeId = Codings.codingKeyId AND
      Codings.languageId = @languageId
   LEFT OUTER JOIN Codings as Codings_2 ON 
      Recipes.categoryId = Codings_2.codingKeyId AND
      Codings_2.languageId = @languageId
   LEFT OUTER JOIN Codings as Codings_3 ON
      Recipes.continentId = Codings_3.codingKeyId AND
      Codings_3.languageId = @languageId
   LEFT OUTER JOIN CodingsAssociated ON
      Recipes.countryId = CodingsAssociated.codingKeyId AND
      CodingsAssociated.languageId = @languageId 
   LEFT OUTER JOIN Codings as Codings_4 ON
      Recipes.typeOfPreparationId = Codings_4.codingKeyId AND
      Codings_4.languageId = @languageId
   LEFT OUTER JOIN Codings as Codings_5 ON
      Recipes.flavourId = Codings_5.codingKeyId AND
      Codings_5.languageId = @languageId
   LEFT OUTER JOIN Codings as Codings_6 ON
      Recipes.preparationSkillId = Codings_6.codingKeyId AND
      Codings_6.languageId = @languageId
   LEFT OUTER JOIN Codings as Codings_7 ON
      Recipes.seasonId = Codings_7.codingKeyId AND
      Codings_7.languageId = @languageId
   LEFT OUTER JOIN RecipesTranslations ON
      Recipes.recipeId = RecipesTranslations.recipeId AND
      RecipesTranslations.languageId = @languageId
   LEFT OUTER JOIN Users ON
      Recipes.userId = Users.userId ;

null id选择行的内连接

2 个答案: